Condensed Financial Information - Statement of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating activities:
Net income	$ 25,597	$ 69,578	$ 63,158
Adjustments to reconcile net income to net cash provided by (used in) operations:
Dividends received from subsidiaries	45,000	40,000	25,000
Other	19,569	4,656	3,833
Net cash provided by (used in) operating activities	118,338	118,221	103,910
Fixed maturities, available-for-sale
Sales	666,976	1,191,796	473,913
Purchases	(803,568)	(1,439,725)	(728,216)
Equity securities
Sales	73,590	6,942	18,899
Net increase in short-term investments	30,384	22,713	47,821
Net cash provided by (used in) investing activities	66,006	(36,461)	(92,773)
Financing activities:
Purchase of treasury stock	(90,866)	(51,980)	(6,756)
Purchase of Senior notes			(7,000)
Proceeds of stock issued from employee stock purchase plan	945	868	727
Proceeds of stock issued from exercise of stock options	1,169	611	944
Net cash provided by (used in) financing activities	(88,752)	(50,501)	(12,085)
Increase (decrease) in cash	95,592	31,259	(948)
Cash at beginning of year	31,768	509	1,457
Cash at end of period	127,360	31,768	509
Parent Company
Operating activities:
Net income	25,597	69,578	63,158
Adjustments to reconcile net income to net cash provided by (used in) operations:
Equity in undistributed net income of wholly-owned subsidiaries	(32,524)	(74,914)	(67,374)
Dividends received from subsidiaries	45,000	40,000	25,000
Other	5,831	4,543	4,682
Net cash provided by (used in) operating activities	43,904	39,207	25,466
Fixed maturities, available-for-sale
Sales	45,716	26,313	9,103
Purchases	(9,253)	(28,213)	(34,932)
Equity securities
Sales		2,995
Purchases		(2,367)
Net increase in short-term investments	10,064	5,122	13,863
Net cash provided by (used in) investing activities	46,527	3,850	(11,966)
Financing activities:
Capital contribution			(2,000)
Purchase of treasury stock	(90,866)	(51,980)	(6,756)
Purchase of Senior notes			(7,000)
Proceeds of stock issued from employee stock purchase plan	945	868	727
Proceeds of stock issued from exercise of stock options	1,169	611	944
Net cash provided by (used in) financing activities	(88,752)	(50,501)	(14,085)
Increase (decrease) in cash	1,679	(7,444)	(585)
Cash at beginning of year	1,646	9,090	9,675
Cash at end of period	$ 3,325	$ 1,646	$ 9,090